Makeclothe->Makehuman tr
We've find explanation about this strange effect.
If we open the file in an old blender version (before 2.77), export it using "old makeclothes" into "old makehuman" (1.0); everything's OK.
If we update Makeclothe we have strange triangles at neck level and if we update makeclothes, we loose texture (file not found).

In order to solve that:
1) update everything (Blender, Makeclothes and MakeHuman)
2) open a new project in Blender
3) Append the clothes in Blender (so don't "Open" but "Append")
4) Export using Makeclothes
5) Open in MakeHuman 1.1.0
And everything's OK!